Sand circulation oven for ball-shaped products



Nov. 11, 1969 M. TAMALET 3,477,703

SAND CIRCULATION OVEN FOR BALL-SHAPED PRODUCTS Filed Jan. 12, 1968 5Sheets-Sheet 1 m 'l", H

MICHEL TAMALET MUFFIN l M. TAMALET Nov. 1 l, 1969 SAND CIRCULATION OVENFOR BALL-SHAPED PRODUCTS Filed Jan. 12, 1968 3 SheetS -Sheet 2 NHLHEL'mqmzr.

6a 0 WklllnM-LL P321? M. TAMALET Nov. 11, 1969 SAND CIRCULATION OVEN FORBALL-SHAPED PRODUCTS Filed Jan. 12, 1968 3 Sheets-$heet 3 mum rmmner.

United States Patent 92,129 Int. Cl. F27b 15/00; F28d 13/06 U.S. Cl.26340 18 Claims ABSTRACT OF THE DISCLOSURE A sand-circulation oven forthe continuous heat treatment of ball-shaped products, characterised inthat said products are carried through the oven while a materialconsisting of fine particles, such as sand, is circulated through saidproducts in order to produce a heat transfer between said products andsaid material.

This invention relates to a sand-circulation oven of the type designedfor heating miscellaneous products in the form of balls. The term ballis used herein for designating any product in the form of relativelylarge granules of substantially spherical configuration. Thecharacteristic dimension of these balls may range from A" or A to about4". The granules may result either from the crushing of larger lumps orblocks, or from a ball press or a ball-producing drum or cylinder. Onthe other hand, the term sand denotes herein any desired relativelyfine-grained material of a size of, say, less than 0.04".

It is known that a bed of products in ball form, laid upon a grate orgrid cannot, retain fine sand deposited on this ball bed. The sand flowis improved if the balls and sand differ considerably in size and if thesupporting grid is vibrated.

The oven constituting the subject-matter of the present invention isbased on this physical phenomenon and characterised in that theball-shaped products are submitted to variable accelerations while thefine-grained or sand material is circulated through said balls in orderto cause the transfer heat therebetween.

The specific heating method according to this invention is particularlysuited for products distilling volatile substances when heated,especially if the pollution and dilution of these volatile substancesmust be avoided to improve their recovery rate.

According to a specific form of embodiment of this invention an oven ofthe type set forth hereinabove comprises: a continuous or endless chainmesh-belt or grid, divided into one or several sections disposedhorizontally or inclined, to which variable accelerations are impressed,and adapted to carry the ball products; one or a plurality of upperdistributors for depositing sand upon the top of the ball bed; means foradjusting the sand circulation rate through said ball bed; a fluidizedbed fed with the sand having passed through the ball bed, and means forlifting the sand back into the upper distributor.

According to a specific feature characterising this invention afluidized loop causes the sand to circulate in counter-currentrelationship to the ball-shaped products, whereby the heat resultingfrom the cooling of said balls can be recovered.

According to this invention the oven comprises several zones, namely apreheating zone, a heating zone and a cooling zone, and each zone isadapted to recycle the sand from the fluidized channel. This channelextends through the combustion chamber and circulates in counter-currentrelationship With respect to the ball products carried by the grid, thecirculation for heat-recovery pur ice pose being independent of the sandcirculation through the ball charge.

According to a modified form of embodiment the above-defined oven zonesare coupled in series, the sand being picked up from the bottom of eachzone by a hopper and lifted back to the top distributor or distributors.

,The combustion chamber of the oven may operate for example by usingburners immersed in the fluidized bed for delivering the heat necessaryfor heating the charge, a cyclone being provided for exhausting thesmoke from the burners. The combustion chamber may advantageouslycomprise baflle means so arranged in. the fluidized bed as to impartchanges of direction to the particles whereby the complete particle flowcan be heated homogeneously.

The sand may further be heated outside the oven, in aninternal-combustion fluidized bed, or in a smoke-flow oven, or in arotary oven. Furthermore, it can be heated by the ducts used for liftingthe particles, these ducts receiving in this case the hot smoke directlyfrom a burner.

According to a specific form of embodiment of the oven according to thisinvention means are provided for collecting and utilizing, withoutdilution, or with a metered dilution, the combustible vapors from thedistillation process of the ball-shaped products and/or their binder.

Other features and advantages of this invention will appear as thefollowing description proceeds with reference to the attached drawingsgiven by way of illustration, it being understood that manymodifications can be brought thereto without departing from the spiritand scope of the invention. In the drawings:

FIGURE 1 is a vertical sectional and elevational view of a typical formof embodiment of an oven according to this invention, the section beingtaken along the line 11 of FIGURE 3;

FIGURE 2 is a plan view of the oven illustrated in FIGURE 1;

FIGURE 3 is a section taken upon the line 33 of FIGURE 1;

FIGURE 4 is a section taken along the line 4-4 of FIGURE 2;

FIGURE 5 is a section taken along the line 5-5 of FIGURE 2;

FIGURE 6 is a diagrammatic section showing a typical example of meansfor lifting the sand back to the upper distributor;

FIGURE 7 is a diagrammatic illustration of a sand circulation path inthe oven;

FIGURE 8 illustrates also diagrammatically a typical example of a sandcirculation path in the oven; and

FIGURE 9 illustrates diagrammatically a method of recovering fuel vaporsfrom the distillation of the ball products and/or their binder.

Referring to the drawings and more particularly to FIGURES 1 and 2, itwill be seen that the ball-shaped products B circulate from left toright as seen in these figures. They are carried by an inclined grid,which may either consist of a single plane or, alternately, of a steppedstructure to permit the periodic exposure of different portions of theproduct and also the loosening of clods. This grid may also be disposedhorizontally, if desired. In the example illustrated it consists of aplurality of successive sections 11, 12, 13 and 14. This grid issubjected to variable accelerations obtained for example by usinghydraulic actuators or piston-cylinder units 16. The cylinders of theseactuators are secured to the frame structure 17 supporting the grids andtheir piston rods are attached to fixed points, or vice versa. The framestructure 17 of these grids is supported by rollers such as 18, 18'disposed at spaced intervals, externally of the oven, like the actuators16. These rollers 18, 18 are provided with shafts rigid with a fixedframe 19 supported by the ground and supporting the installation. Therelative spacing of the grid-forming bars is determined with a view toprevent any jamming of the products B. The balls circulating on the topof grids 11 to 14 are retained laterally by vertical side walls 24 and24.

The inclination and the accelerations imparted to the grid may be suchthat products B are free from any frictional contact or shocks with thegrids. The frequency and amplitude of the accelerations permit ofadjusting the feed rate of the products.

Fixed scrapers having fingers adapted to extend through the grid barsare provided for avoiding any clogging thereof. The fingers 20 of one ofthese scrapers are illustrated which co-act with the bars of grid 13.

The sand S is discharged upon the top of the ball layer B, throughoutthe length thereof, from a number of upper distributors such as the onedesignated by the reference numeral in the drawing. This distributor 15comprises a fixed upper casing 21 into which an inlet duct 22 dischargessand recovered from the oven, as will be described presently in detail,and an outer sleeve 23 adapted to be adjusted vertically along thedistributor axis for altering at will the distance from the bottom ofthe distributor to the grid, i.e. the height of the natural angle ofrepose of the sand heap formed above the charge, and therefore formodifying at will the amount of sand dispensed upon the ball bed.

This sand is retained laterally by the walls 24, 24' of the housingsupporting the grids, and at either end sand joints 25, 26 are providedfor sealing the oven enclosure 27 in which the charge B and the sand Sflowing therethrough circulate for producing the desired heat transfer.

The sand circulation output through the charge B is adjustable forexample by means of a double series of horizontal plates 28 and 28'disposed at right angles to the direction of flow of the ball productsand disposed beneath each grid. These movable plates 28, 28' are adaptedto slide on each other and act as diaphragms actuated either manually bymeans of a handle 29 (FIG- URE 3) or by using servo-motor means in orderto maintain the temperature of the charge B at a predetermined value.

After having passed through the bed of ball products B the sand fallsinto a plurality of hoppers such as 30 disposed beneath the grids andadapted to feed a fluidized bed 31. A particle aspirator or trompe isprovided at the bottom of each hopper for feeding each upper distributor15. Each aspirator or trompe consists of two coaxial tubes 32, 33,respectively, capable of directing the sand pneumatically up to the duct22 feeding the distributor 15. A cyclone or like scrubber 34 is arrangedin the distributor for separating completely the particles from thesuction air stream delivered via the tube 33.

Means are provided for adjusting the sand level in the upperdistributors 15. These means, consisting for example of electriccontacts, are disposed in each upper distributor 15 and capable ofdetecting the upper and lower level of the sand in order to actuate inthe all or none manner the means supplying fluid to the particle-suckingtrompe or aspirator. Any suitable servo device may be used forcontrolling these means.

The width of the casing limited laterally by the walls 24, 24'corresponds to the width of the grids 11. On the other hand the lengthof this casing will be selected as a function of the permeability of thecharge of ballshaped products and also of the amount of sand to be 4duct 36 by using a supply of compressed gas 38 fed to the bottom of thisduct. An electric switch 37 is provided for discontinuing the supplyingof compressed gas when the sand level in hopper 30 is below apredetermined minimum value.

The manner in which the sand circulates from one Zone to another zone ofthe oven will now be described.

The oven illustrated by way of example in the drawings comprises fourzones (see FIGURE 7):

A preheating zone Z (corresponding to grid 11).

Two heating zones proper Z and Z (corresponding to grids 12 and 13).

A cooling zone Z (corresponding to grid 14).

In this figure there is illustrated diagrammatically a sand circulationpath in the oven.

The ball-shaped products B circulate in the direction of the arrow bafter having been introduced at A. A fluidized loop F causes the sand tocirculate in countercurrent relationship (see arrows s) to the productsB, whereby the heat resulting from the cooling of the balls in zone Zcan be recovered.

Each zone Z to Z is adapted to recycle the sand from the fluidizedchannel (fluidized beds 31 of FIGURES l to 3). A combustion chamber Cdescribed more in details hereinafter and operating for example withimmersed burners, will supply the heat required for heating the charge.

The sand arriving at the end of the fluidized loop F flows over a chuteand falls into a storage hopper T. This chute permits of maintaining thefluidized bed 31 (FIGURE 1) at a constant level. The function of hopperT is to maintain a certain reserve of sand for operating the plant andalso to store the particles when the oven is inoperative or held up forany reason. A suction trompe or aspirator R is dipped into this hopperand feeds the loop inlet. The output of this trompe will regulate thetotal sand circulation in the loop F. The output should be so adjustedas to ensure the best possible heat recovery, this requirement being metwhen the heat storage capacity of the sand nearly equals that of theball products.

If the ball-shaped products requires a stronger cooling, the sand in thereturn channel of the fluidized loop F may be cooled for example byusing water or steam piping, or a water vaporization carried outdirectly Within the fluidized bed.

In the example illustrated in FIGURE 7 the recovery circulation isindependent of the sand circulation through the charge B. On the otherhand, in the alternate form of embodiment of the invention illustratedin FIGURE 8 the four zones Z to Z; are coupled in series. The sandpicked up from the bottom of each zone by a hopper is lifted by a trompeor aspirator for example of the type shown in FIGURE 6 and to bedescribed presently.

This form of embodiment is more economical but at the expenses of theflexibility of the installation. Of course, it would not constitute adeparture from the spirit and scope of the invention to contemplateother modifications, for example, the one consisting in coupling saidzones Z to Z by pairs. Moreover, although this specification refers to afour-zone oven, it is clear that the number of zones of the oven may beincreased or reduced without departing from the basic principle of theinstallation constituting the subject-matter of this invention.

Now the method utilized for heating the sand will be described withreference to FIGURES 1 to 5 of the draw- The combustion chamber of theoven according to this invention comprises two immersed burners 39 and40 dipping into the fluidized bed 31.

A cyclone 41 is provided for sucking the smoke from the two burners 39and 40 and exhausting it to the outside through a vent duct 42. Thecombustion chamber comprises in the fluidized bed 31 batfle means suchas 43 adapted to impart to the particles a movement shown by the arrowsof FIGURE 2, in order homogeneously to reheat the flux of theseparticles.

A larger installation would require, of course, a greater number ofburners. Besides, the sand could be heated externally of the oven,without departing from the present invention, by using a fluidized,internal-combustion bed, or a smoke-stream bed, or alternately a rotaryoven, but it is clear that these suggestions should not be construed aslimiting the invention.

If the sand became more or less smoothed by its contact Withstheball-shaped products, one fraction of the sand may be heated at a highertemperature to eliminate the pollution therefrom. This fraction issubsequently mixed with the main mass of sand.

In the oven proper the sand may further be heated by the trompes oraspirators used for lifting the particles (and consisting of the ductsor tubes 32 and 33 shown in FIGURES 3 and 5). In this case the hot smokefrom a burner is fed directly to the trompes or aspirators. Thecombustible fluid and air may then be brought just to the lower end ofthe trompe which in this case will act itself as a burner.

The oven according to this invention may advantageously be provided withmeans for recovering gases from processes applied to ball-shapedmaterials or products. Thus, for example, if the oven is used forreducing the smoke content of coal, or treating agglomerated products inwhich tar, pitch and/or bitumen is used as a binder, volatile substancesare released either from the products themselves, or from their binderor binders. These volatile substances are combustible and consist of agaseous mixture of hydrogen, CH etc., and also of tar vesicles orbubbles.

In most of the known plants of this kind these products arelost iftheycannot be burned immediately. Besides, particular attention mustalso be paid to the fact that they cannot be exhausted through thechimney to the atmosphere without raising atmospheric pollutionproblems.

The advantage of using a sand circulation oven is to prevent thedilution of these combustible vapors, whereby they can become a gashaving a high heating power which is easy to burn as such.

FIGURE 9 illustrates diagrammatically the manner in which thesecombustible vapors can be recovered. These vapors are sucked at 45 anddirected into the enclosure 28 (FIGURE 1) by a suction 'fan 44 (FIGURE9) through heat-insulated pipe lines 45. At the same time a pressureslightly in excess of the atmospheric value is maintained in the ovenchamber 27; a by-pass valve 46 is provided for adjusting the pressurewithin the oven. The vapors thus discharged through the duct 47 aredirected to the burners of this oven, the excess being burned if desiredin a near-by boiler.

A slight dilution may promote the extraction of these combustiblevapors. In this case a pre-adjusted smoke output will be fed into theoven by means of rows of noizles provided to this end.

To avoid any ingress of air the oven is sealed by means of bellows suchas 48 and 49 disposed at either end thereof (see FIGURES l and 2).Moreover, the upper housing of the sand distributor is constantly keptunder pressure to prevent the ingress of carrier fluid. The fluidizedbeds circulate in closed casings.

The fluidizing gas can escape either through orifices such as 50 formedin the outer tube 32 of the trompe, or from the end of the cold channeltowards the storage hopper (denoted by the reference letter T in FIGURE7). On the other hand, the sand column formed at the bottom of bachhopper 30 will limit considerably the ingress of fluid.

If the gases released during the process are of combustible nature, thefluidized beds and the trompes are supplied with scrubbed smokes withoutany oxygen content in order to avoid a detrimental air input likely todevelop detonating mixtures. Moreover, it is clear that the ovenconstituting the subject matter of this invention can be used forprocessing products in atmospheres of predetermined composition.

Regarding the specific nature of the products to be treated, theabove-described oven is capable of processing all products in the formof balls or granules of such dimensions that sand can flowtherethrouglh. These products may. consist for example of ore pellets,agglomerated ores,-with qr without binder, agglomerated coal forroasting torrefaction, etc.

During the treatment, these products may go through a plasticdeformation phase, as in the case of certain coals. In this case it ispossible to arrange under one or more metal grids a metal platepreventing any flow of the sand along a predetermined zone length. Thus,the products are maintained without any deformation in a fixed bed. Theamount of heat transferred from the sand enables the products to clearthe critical temperature.

The nature of the sand will be selected as a function of tlie oventemperature in order to obtain a satisfactory resistance to thistemperature and to erosion. The sand granulometry will be such that itwill circulate and flow freely through the charge.

In the case of ore roasting applied to ball-shaped or pellet ore, theore itself sieved to the proper granulometry may be used as sand. Thefines from the oven will be directed to the ball-forming device. In theoven the sand will be sieved before penetrating into the storage hopperin order to eliminate abnormally large granules from the charge.

According to another form of embodiment of the oven of this invention,given by way of example, the oven may be anintegral part of an assemblycomprising the apparatus for agglomerating the coal or ore into balls.The finished products, before the agglomeration step, require a dryingstep which may be performed by circulating the product, prior to itsagglomeration, through a bed of balls during the cooling thereof.

The oven according to this invention is characterised by manyadvantageous features of which some are listed herebelow:

The products are treated or processed continuously;

The heating can take place very rapidly due to the very greatgas-to-particles heat transfer surface area and to the solid-to-solidheat transfer;

The particularly simple method of recovering heat from the productsbeing cooled;

The absence of difiiculty in the recovery and combustion of volatilevapors from the distillation of the products or their binders, wherebythe problem of atmospheric pollution is solved at the same time.

In conventional ovens designed for processing ballshaped products(convection oven), the products are heated by circulating a gas throughthe bed. The heat transfers require the use of a very large volume ofgas and are therefore attended by a considerable dilution of the gasesreleased during the process, so that these gases are hardly recoverable,especially if they are of combustible nature.

Besides, since the continuously-vibrating grid supporting the productsto be processed is at a substantially constant temperature, heat cyclesdetrimental to the stability of the products are safely avoided.

Of course, although the present invention has been described inconjunction with preferred embodiments, it is to be understood thatmodifications and variations may be resorted to without departing fromthe spirit and scope of the invention, as those skilled in the art willreadily understand. Such modifications and variations are considered tobe within the purview and scope of the invention and appended claims.

What is claimed is:

1. An oven for securing a heat transmission between a material of finegrain or sand and products in the form of balls comprising an uppercasing whose bottom is formed by a grill which carries the bed ofproducts in the form of balls, hydraulic jacks giving to said grillvariable accelerations, upper distributors distributing sand throughoutthe entire length of said bed of balls, funnels located under said grillfor receiving said sand after traversing said bed of balls and saidgrill, a lower casing fed by said funnels and containing the sand in theform of a fluidized bed in which the sand is reheated and a particleconveyance located at the foot of each of said funnels for a pneumatictransport of the sand to said upper distributors.

2. An oven as set forth in claim 1 in which said grill is inclined tothe horizontal and is formed of several successive elements.

3. An oven as set forth in claim 1 in which there are provided fixedscrapers whose fingers pass across the bars of said grill.

4. An oven as set forth in claim 1 wherein burners are submerged in saidfluidized beds for heating the sand and a cyclone is provided forremoving the fumes of said burners and rejecting it towards theexterior.

5. An oven according to claim 4 wherein baflies are provided in saidfluidized beds for giving to said particles changes in directionallowing reheating the flux of the sand particles in a homogeneous way.

6. An oven as set forth in claim 1 wherein said particle conveyance isfed directly by the heated fumes of a burner in order to heat the sand.

7. An oven according to claim 1 wherein there is provided under saidgrill carrying said ball products a double play of perforated plates andmeans for sliding one upon the other in order to adjust the circulationflow of the sand across said ball products, said play of movable platesforming diaphragms actuated manually.

8. An oven according to claim 1 comprising for the return of the sand indiluted phase at the lower portion of each funnel a column provided atits foot with a means for receiving compressed gas, an electricalcontact being provided in order to cut the feed of compressed gas whenthe level of sand in a funnel is too low.

9. An oven as set forth in claim 1 in which said fluidized beds define afluidized loop for the circulation of said sand, said loop comprising areturn channel provided at its end with an outlet and a stock tunnelreceiving said sand, said oven comprising a tube for feeding said returnchannel and maintaining said fluidized beds at a constant level.

10. An oven according to claim 1 comprising a ventilator for sucking thecombustible vapors coming from the thermic treatment of the products inthe form of balls; a valve for adjusting the pressure in said oven at avalue slightly above that of the exterior atmosphere and a conduit forevacuating said vapors and leading themto burners serving to heat thesand.

11. An oven according to claim 1 in which said upper casing comprises ateach of its ends air tight bellows and said lower casing is a closedcasing.

12. An oven as set forth in claim 1 in which the exterior tube of thefunnels for the particles is provided with orifices for the escape ofthe fluidization gas of said fluidized beds.

13. An oven as set forth in claim 10 in which there is provided anadjusted flow of the fumes in order to facilitate the extraction of thecombustible vapors.

14. An oven as set forth in claim 1 in which said fluidized beds andsaid funnels for the particles are fed by dust free fumes and withoutoxygen.

15. An oven as set forth in claim 1 in which a portion of the sand isheated to a high temperature and then mixed with the remainder.

16. An oven as set forth in claim 1 in which there are provided aplurality of zones, said zones respectively preheating said products inthe form of balls, heating and cooling, with each zone recycling thesand coming from the fluidized beds.

17. An oven according to claim 4 in which said burners are fed by thegas products during the course of treatment.

18. An oven as set forth in claim 1, in which there is deposited uponthe grill supporting the products in the form of balls when the latterduring the course of treatment are fractured into a phase of plasticdeformation, a metallic plate preventing all flow of sand upon a portionof said grill.

References Cited UNITED STATES PATENTS 2,592,783 4/1952 Aspegren 165-1072,900,179 8/ 1959 Kaufmann. 3,053,704 9/ 1962 Munday.

JOHN J. CAMBY, Primary Examiner US. Cl. X.R. l65104

